Sensor for measuring carbon dioxide in respiratory gas

ABSTRACT

A sensor main unit  1  is axially split into three sub-segments. A light-emitting element  2  is attached to one end portion, and a light-receiving element  3  is attached to the other end portion. A respiratory flow path  4  is formed so as to penetrate through the center portion. The sensor main unit  1  is attached to a position on the face below the nostrils, and respiratory gas from the nostrils is guided into the respiratory flow path  4  and is caused to cross over the optical axis connected the light-emitting element  2  and the light-receiving element  3 , thereby measuring a carbon dioxide gas in the respiratory gas.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 10/092,591 filed Mar. 8,2002, which claims priority under 35 USC 119 from Japanese PatentApplication Nos. 2001-064901, 2001-107179 and 2002-46480. The entiredisclosures of the prior applications are incorporated by referenceherein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sensor for measuring theconcentration or presence/absence of carbon dioxide in respiratory gasthrough the nostrils or mouth of a living body. More particularly, theinvention relates to a simple, compact sensor for measuring carbondioxide in respiratory gas which can improve the accuracy in measurementand response.

2. Related Art

In general, when the concentration of carbon dioxide contained inrespiratory gas from a living body is optically measured, therespiratory gas is caused to pass through a cylindrically-shaped airwayadapter. An infrared ray is radiated onto the respiratory gas from alight-emitting element. A voltage corresponding to the amount of lightwhich is absorbed by carbon dioxide contained in the respiratory gas isdetected by a light-receiving element, thus measuring the concentrationof carbon dioxide.

FIG. 16 shows the schematic configuration of an example of such arelated capnometer. As shown in FIG. 16, one end 101 a of an airwayadapter 101—which is formed into a substantially cylindrical shape andthrough which respiratory gas passes—is to be connected to a tubeinserted into a trachea of a patient. Another end 101 b is to beconnected to a Y piece of a respiratory circuit, such as a ventilator.An intermediate portion of the airway adapter 101 has a rectangularcross-sectional profile. Circular windows 101 c, 101 d are formed inrespective, mutually-opposing surfaces of the intermediate portion suchthat the windows are concentrically aligned with each other. A sensormain unit 102 is removably attached to the intermediate portion of theairway adapter 101.

The sensor main unit 102 is formed into a rectangular-parallelepipedshape, and a U-shaped notch is formed in an intermediate portion of thesensor main unit 102. The intermediate portion of the airway adapter 101is to be fittingly attached to the notch. Two mutually-opposing surfacescome into contact with the windows 101 c, 101 d of the airway adapter101. A light-emitting element 103 emitting a infrared light is disposedon one side with reference to the notch formed in the sensor main unit102.

A filter 104 for absorbing only light having wavelength to be absorbedby carbon dioxide and a light-receiving element 105 are disposed on theother side with reference to the notch formed in the sensor main unit102. The light-emitting element 103 and the light-receiving element 105are connected to a monitor main unit 107 via a lead wire 106. Theintermediate portion of the airway adapter 101 can be removably attachedto the sensor main unit 102.

In the related capnometer having the foregoing configuration, lightemitted from the light-emitting element 103 enters the light-receivingelement 105 by way of the window 101 c, the respiratory gas in theairway adapter 101, the window 101 d, and the filter 104. The quantityof light corresponding to the concentration of carbon dioxide isdetected by the light-receiving element 105. An output signal from thelight-receiving element 105 is input to the monitor main unit 107, wherethe concentration of carbon dioxide is displayed.

In the related-art example, the airway adapter 101 through whichrespiratory gas passes is attached to the sensor main unit 102. Arelated-art capnometer has a structure in which a sampling tube isconnected to a sensor main unit disposed in the monitor main unit 107.In this case, one end of the sampling tube which aspirates part ofrespiratory gas is connected to the airway adapter 101 through which therespiratory gas passes. The other end of the sampling tube is connectedto the monitor main unit 107. A pump is disposed in the monitor mainunit 107, and respiratory gas is led to the sensor main unit disposed inthe monitor main unit 107.

U.S. Pat. Nos. 5,099,836 and 5,335,656 describe other types of relatedrespiratory gas sensors. U.S. Pat. No. 5,099,836 shows a partiallycutaway top view shown in FIG. 17. As shown in FIG. 17, the inside of atubular nasal cannula 201 is separated into a first separate chamber 203and a second separate chamber 204 by a wall 202. One end of the wall 202is connected to one side of an interior surface of the nasal cannula201, and the other end of the same is connected to the other side of theinterior surface, thus hermetically separating the two separate chambers203, 204 from each other. Nasal tubes 205, 206 to be inserted intorespective nostrils project in parallel with each other from an outerperiphery of the nasal cannula 201. The inside of the nasal tube 205 isseparated into passageways 205 a, 205 b by the wall 202 extending fromthe inside of the nasal cannula 201. Similarly, the inside of the nasaltube 206 is separated into passageways 206 a, 206 b by the wall 202. Thepassageways 205 a, 206 a are in communication with the first separatechamber 203, and the passageways 205 b, 206 b are in communication withthe second separate chamber 204.

An oxygen gas supply tube 207 is connected to one end of the firstseparate chamber 203 of the nasal cannula 201. A tubing 208 is connectedto one end of the second separate chamber 204 for sensing the user'sbreathing pressure. An oxygen cylinder is connected to the tube 207through a pressure control valve (not shown). The tubing 208 isconnected to a pressure transducer (not shown).

There may be a case where the tubing 208 is used as a sampling tube andconnected to a carbon dioxide sensing monitor (not shown) to measure theconcentration of carbon dioxide in respiratory gas.

In relation to the apparatus for detecting respiratory gas configured inthe manner as mentioned above, the oxygen supplied from the oxygencylinder through the tube 207 is fed to the nostrils through the firstseparate chamber 203, the passageway 205 a of the nasal tube 205, andthe passageway 206 a of the nasal tube 206. Part of exhaled gas from thenostrils is discharged to the tubing 208 through the passageway 205 b,206 b and the second separate chamber 204, and the breathing pressureand the concentration of carbon dioxide are detected.

As shown in FIG. 18, U.S. Pat. No. 5,335,656 relates to a nasal cannulae301 which has a tubular body, is to be attached to the skin in thevicinity of the nose, supplies a treating gas to the nostrils, andmeasures the concentration of carbon dioxide in respiratory gas. Aseptum 302 is disposed in the nasal cannulae 301 to define an inhalationmanifold 303 and an exhalation manifold 304. A flexible tubing segment305 is connected to one end of the nasal cannulae 301 for supplying atreating gas to the inhalation manifold 303. A flexible tube segment 306is connected to the other end of the nasal cannulae 301 for aspiratingthe exhaled gas from the exhalation manifold 304.

A nasal prong 307 is connected to the inhalation manifold 303 forsupplying the gas to a first nostril. The exhalation manifold 304 isconnected to and is communicated with a nasal prong 308 which is fittedto a second nostril to aspirate the exhaled gas. The segment 306 isconnected to a carbon dioxide measurement sensor (not shown) whichmeasures the partial pressure of carbon dioxide in the exhaled gas.

The related capnometer shown in FIG. 16 requires the airway adapter 101.The airway adapter 101 is connected to an endotracheal tube and a Ypiece. Hence, difficulty is encountered in connecting the apparatus to apatient to whom no endotracheal tube is attached. Further, the apparatusis bulky, expensive, and complicated in construction. Further, theairway adapter 101 must be replaced, thus increasing operating costs.The light-emitting element 103 has hitherto involved power consumptionof 1 W or more. Hence, the sensor main unit 102 becomes hot. If theapparatus is designed so as to come into direct contact with the skin,the apparatus will remain in contact with the skin for a long period oftime for measurement, thus posing a risk of heat injury.

When the tubing shown in FIG. 17 is used, there arises a problem of thetubing is clogged with moisture in respiratory gas after long-term use.Further, the detection tube is disposable, thereby adding to operatingcosts. When the tubing is used as a sampling tube, there arises a timelag until the time carbon dioxide gas is detected, because the length ofthe tubing is usually 2 meters or more. Hence, detecting responsebecomes slow, which in turn deteriorates detection accuracy.

According to the related-art example shown in FIG. 17, if one of thepair of nostrils into which the nasal tubes 205, 206 are inserted hasbeen clogged, the tube inserted in the thus-clogged nostril comes tosample air. The concentration of carbon dioxide gas in a sampledrespiratory gas becomes about one-half the actual concentration inrespiratory gas, which in turn may cause an error in measurement.Further, in the related-art example shown in FIG. 18, if the nostrilinto which the nasal prong 307 of the inhalation manifold 303 isinserted has been clogged, a treating gas cannot be supplied to a livingbody. In contrast, if the nostril into which the nasal prong 308 of theexhalation manifold 304 is inserted has been clogged, detection ofcarbon oxide gas becomes impossible.

SUMMARY OF THE INVENTION

The present invention has been conceived against such a problem and aimsat providing a compact, inexpensive sensor for measuring carbon dioxidegas in a respiratory gas which can accurately detect the concentrationof carbon dioxide gas even when one of a pair of nostrils has beenclogged, improve measurement accuracy and responsibility, and curtailoperating costs.

In order to achieve the object, there is provided a sensor for measuringthe concentration or presence/absence of carbon dioxide in respiratorygas from a living body, comprising:

a support member for supporting a light-emitting element and alight-receiving element which are disposed on a single optical axis soas to oppose each other; and

a respiratory flow path formed in the support member in such a mannerthat the respiratory gas can flow so as to cross over the optical axiswhen the support member is attached to an area located below thenostrils of the living body.

In the present invention, the sensor further comprises retaining meansfor attaching and securing the support member to a position below thenostrils.

In the present invention, retaining means corresponds to ear strapswhich are hooked around the ears of the living body for holding.

In the present invention, the ear straps includes at least one of afirst lead wire for supplying power to the light-emitting element and asecond lead wire for outputting a signal detected by the light-receivingelement to the outside such that at least one of first and second leadwire is laid in the ear straps.

In the present invention, the retaining means corresponds to anengagement member provided on the support member and engaged with atubular member for supplying oxygen to the nostrils.

In the present invention, the retaining means is an oxygen mask whichcovers the face of the living body and supplies oxygen.

In the present invention, the support member is provided with arespiratory guide section for guiding the respiratory gas from thenostrils to the respiratory flow path.

In the present invention, the support member is provided with an adapterhaving nasal prongs to be inserted into the nostrils for introducing therespiratory gas from the nostrils to the respiratory flow path.

In the present invention, the support member is provided with arespiratory guide section for introducing the respiratory gas from themouth to the respiratory flow path.

In the present invention, there is provided a sensor for measuring theconcentration or presence/absence of carbon dioxide in gas respiratoryfrom a living body, comprising:

a support member for supporting a light-emitting element and alight-receiving element which are disposed on a single optical axis soas to oppose each other;

a respiratory flow path formed in the support member in such a mannerthat the respiratory gas can flow so as to cross over the optical axis;and

an oxygen mask covering the face of the living body and supplies oxygen,

wherein the support member is provided on an exterior surface of theoxygen mask to bring the inside of the oxygen mask in communication withthe respiratory flow path.

In the present invention, the light-emitting element is a miniatureinfrared radiation lamp having a power consumption of 0.3 W or less.

In the present invention, there is provided a sensor for measuring theconcentration or presence/absence of carbon dioxide in respiratory gasfrom a living body, comprising:

an airway case opened on both ends thereof and having at least acircumferential wall having a hole formed therein for passing throughthe respiratory gas; and

a pair of holding members for hermetically holding transparent thinfilms between respective end faces of the airway case;

a pair of supporting members respectively fitted into the outer endfaces of the pair of holding members, for supporting a light-emittingelement and a light-receiving element which are disposed on a singleoptical axis so as to oppose each other,

wherein the airway case is attached to a position below the nostrils ofthe living body, the respiratory gas can cross over the optical axis.

In the present invention the thin films are anti-fogging films forpreventing condensation of moisture in the respiratory gas on thesurfaces of the films.

In the present invention, a pair of supporting members are removablyengaged with a pair of holding members through engagement members.

In the present invention, the airway case is provided with an adapterhaving nasal prongs to be inserted into the nostrils for introducingrespirator gas from the nostrils into the airway case.

In the present invention the airway case has a respiratory guide sectionfor introducing respiratory gas from the mouth into the airway case.

According to the present invention, there is provided a respiratory gasfrom a living body can be guided directly to an optical axis of a sensorthrough a respiratory flow path provided in the sensor. Hence, there isobviated a necessity for an airway adapter and a sampling tube, whichhave hitherto been employed, thereby rendering the sensor compact andless expensive. Even if one of the nostrils becomes clogged, theconcentration of carbon dioxide gas can be detected accurately, therebyimproving measurement accuracy and responsibility.

According to the present inventions, a cylindrical member through whichrespiratory gas flows and a support member for supporting alight-emitting element and a light-receiving element are formedseparately and removably from each other. Hence, production of acylindrical member is facilitated, as is cleaning of the cylindricalmember. Moreover, thin films are hermetically interposed between thecylindrical member and the support member by holding members. Hence, solong as the thin films are formed from a anti-fogging film, occurrenceof clouding due to moisture in respiratory gas can be prevented, therebyenabling accurate measurement of concentration of carbon dioxide gas inthe respiratory gas.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a transverse cross-sectional view showing an exampleconfiguration of a sensor for measuring the concentration of a carbondioxide in respiratory gas according to a first invention;

FIG. 2A is a perspective view showing an overview of one configurationexample of a sensor main unit;

FIG. 2B is a perspective view showing an overview of anotherconfiguration example of the sensor main unit;

FIG. 2C is a perspective view showing an overview of yet anotherconfiguration example of the sensor main unit;

FIG. 3 is a perspective view showing the sensor main unit shown in FIG.1 when the unit is fastened by ears by way of ear straps;

FIG. 4 is a perspective view showing the sensor main unit shown in FIG.1 when the unit is attached to a nasal tube;

FIG. 5 is a perspective view showing a state in which lead wiresembedded in the ear straps shown in FIG. 4 are bundled into one side ofthe sensor main unit;

FIG. 6 is a perspective view showing a state in which an adapter havingnasal prongs is attached to an outer peripheral surface of the sensormain unit shown in FIG. 3;

FIG. 7A is an exploded perspective view showing the principal featuresof the sensor main unit shown in FIG. 6;

FIG. 7B is a front view showing an example of another geometry of thenasal prongs shown in FIG. 6;

FIG. 7C is a front view showing an example of yet another geometry ofthe nasal prongs shown in FIG. 6;

FIG. 7D is a perspective view showing an another example ofconfiguration of the adapter shown in FIG. 6;

FIG. 7E is an exploded view showing the adapter when it is fitted intothe sensor main unit shown in FIG. 7D;

FIG. 8 is a perspective view showing an example of configuration of anexample of a sensor for measuring the concentration of a carbon dioxidein respiratory gas according to the second invention;

FIG. 9 is a perspective view showing the sensor main unit shown in FIG.1 when the sensor main unit is attached to an exterior surface of anoxygen mask;

FIG. 10 is a partially cutaway front view showing an respiratory gasinlet guide when provided at the entrance of a respiratory flow path ofthe sensor main unit shown in FIG. 1;

FIG. 11 is a perspective view showing an air guide for nasal respirationand an air guide for oral respiration provided in the respiratory gasinlet guide shown in FIG. 10;

FIG. 12 is a transverse cross-sectional view showing an exampleconfiguration of the third invention;

FIG. 13 is a longitudinal cross-sectional view shown in FIG. 12;

FIG. 14 is an exploded perspective view shown in part of FIG. 12;

FIG. 15 is a perspective assembly view of the principal features shownin FIG. 12;

FIG. 16 is a descriptive view showing a schematic configuration of anexample of a related capnometer for measuring the concentration of acarbon dioxide gas;

FIG. 17 is a longitudinal cross-sectional view showing an exampleconfiguration of a related-art nasal tube; and

FIG. 18 is a perspective view showing another example configuration ofthe related-art nasal tube.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of a sensor for measuring the concentration of a carbondioxide gas in respiratory gas according to the invention will bedescribed herein below by reference to the accompanying drawings.

FIG. 1 is a transverse cross-sectional view showing an exampleconfiguration of a sensor according to a first invention. As shown inFIG. 1, a sensor main unit 1 which is formed from resin or metal into asubstantially cylindrical shape and serves as a support member isaxially separated into three chambers. A light-emitting element 2 isdisposed in a chamber located at one end of the three chambers, and alight-receiving element 3 is disposed in another chamber located at theother end of the three chambers. An respiratory flow path 4 is formed soas to vertically penetrate a middle chamber of the three chambers. Therespiratory flow path 4 is hermetically separated from the adjacent twochambers by partitions. An opening section is formed in each of thepartitions. A transparent window 5 which permits transmission of lightis hermetically fitted to the opening section formed in the chamberhaving the light-emitting element 2 provided therein and to the openingsection formed in the chamber having the light-receiving element 3provided therein. A filter 6 which permits transmission of only lighthaving a wavelength to be absorbed by a carbon dioxide gas is providedon the light-receiving element 3.

A lead wire 7 is connected to the light-emitting element 2 for supplyingvoltage. A lead wire 8 is connected to the light-receiving element 3 forextracting a detected signal to the outside. The lead wire 7 is retainedby the sensor main unit 1 through a socket 9, and the lead wire 8 isretained by the sensor main unit 1 via a socket 10. The light-emittingelement 2 is constituted of a miniature lamp which radiates infraredrays with power consumption of 0.3 W or less.

FIGS. 2A through 2C show another example configurations of the sensormain unit 1 shown in FIG. 1. FIG. 2A shows an example in which both endsof the sensor main unit 1 are bent so as to match the contour of part ofthe face located below nostrils of a living body. Even in this case, thelight-emitting element 2 and the light-receiving element 3 are alignedwith a single optical axis, spaced a given distance from each other, andsecured to and retained on the sensor main unit 1. In this example, thesensor main unit 1 can be stably retained on the face of the livingbody.

FIG. 2B shows an example in which the sensor main unit 1 is formed intoa rectangular-parallelepiped, the respiratory flow path 4 provided bycutting off the axial center of the rectangular parallelepiped. Here,the sensor main unit 1 may be cylindrical.

FIG. 2C shows an example of the sensor main unit 1: that is, the endsection having the light-emitting element 2 housed therein and the endsection having the light-receiving element 3 housed therein, areconnected together by a plurality of connecting rods: e.g., fourconnecting rods 1 a. In this configuration, even if respiratory gascrosses over an optical path between the light-emitting element 2 andthe light-receiving element 3 at substantially any angles, measurementof the respiratory gas can be effected. Hence, so long as an opticalpath is orthogonal to the flow of the respiratory gas, there isincreased the area for positioning the sensor main unit 1 to be attachedbelow the nostrils.

Next will be described retaining means for retaining the sensor mainunit 1 constructed in the manner mentioned above to a position locatedbelow the nostrils of the face of a subject. FIG. 3 is a perspectiveview showing a first example configuration of the retaining means. Earstraps 12, 13 are connected to the respective ends of the sensor mainunit 1. The lead wire 7 or 8 is embedded in one of the ear straps 12,13, and the remaining lead wire is embedded in the remaining year strap.Hooking the ear straps 12, 13 around ears 14, the sensor main unit 1 isretained in a position located below the nostrils 15. The width (w) ofthe support member in a direction perpendicular to a line (dashed line)extending between the light-emitting element and the light-receivingelement is smaller than a distance between the nostrils and the mouth.

FIG. 4 is a perspective view showing a second example configuration ofthe retaining means. A nasal tube 16 which is a tubular member forsupplying oxygen into the living body is inserted into the nostrils 15of the subject. Tubes 17, 18 are connected to the respective ends of thenasal tube 16 for supplying oxygen. A U-shaped grip 19 serving as anengagement member is formed integrally with an outer peripheral surfaceof the center portion of the sensor main unit 1 so as to project to theoutside.

In this configuration, as a result that the grip 19 of the sensor mainunit 1 is fitted to the outer circumferential surface of the nasal tube16, the sensor main unit 1 can be attached to and retained on a positionbelow the nostrils 15 of the subject. At this time, the tubes 17, 18 ofthe nasal tube 16 are put around the ears 14 of the subject. As shown inFIG. 4, if the ear straps 12, 13 of the sensor main unit 1 are hookedaround the ears 14, the sensor main unit 1 can be retained morereliably. In this state, respiratory gas from the nostrils 15 isintroduced into the respiratory flow path 4 of the sensor main unit 1.The sensor main unit 1 can detect the concentration or presence/absenceof a carbon dioxide gas.

As shown in FIG. 4, there has been described a case where the ear straps12, 13 having the lead wires 7, 8 embedded therein are connected to therespective ends of the sensor main unit 1. As shown in FIG. 5, the leadwires 7, 8 may be bundled into a single wire and may not be put aroundthe ear 14. In this case, the sensor main unit 1 is retained by thenasal tube 16 by way of the grip 19.

In place of using the ear straps 12, 13 shown in FIG. 3, a tape may beused as retaining means for retaining the sensor unit 1 on the face ofthe subject.

As the perspective view shown in FIG. 6, the outer peripheral surface ofthe respiratory flow path 4 formed in the sensor main unit 1 is coveredwith a semi-cylindrical adapter 32 having a pair of nasal insertionprongs 31. In this case, as shown in an exploded perspective view shownin FIG. 7A, the nasal prongs 31 communicate with the inside of theadapter 32, and the respiratory gas from the nose is guided to therespiratory flow path 4 of the sensor main unit 1. As shown in FIG. 7A,the pair of nasal prongs 31 may be separated from each other.Alternatively, as shown in FIG. 7B, the shape of nasal prongs 31 may beletter V. Further, as shown in FIG. 7C, the shape of nasal prongs 31 maybe letter U. Further, as can be seen from a perspective view shown inFIG. 7D, the adapter 32 may be formed into a substantially-cylindricalshape. As can be seen from a perspective view shown in FIG. 7E, theadapter 32 may be inserted into the respiratory flow path 4 of thesensor main unit 1. In this case, an opening section 32 a is formed inthe bottom of the adapter 32 for circulation of respiratory gas.

FIG. 8 is a perspective view showing an example configuration of thesecond embodiment of the invention. In this example, the sensor mainunit 1 is attached to and retained on an interior surface of an oxygenmask 20 attached to the face. As shown in FIG. 8, the oxygen mask 20 isfastened around the ears 14 by bands 21. A pair of annular adapters 22are secured on positions below the nostrils 15 in the oxygen mask 20 soas to oppose each other. The adapters 22 are jointed together by aconnecting rod 23. The grip 19 provided on the sensor main unit 1 isfitted to the connecting rod 23 so that the sensor main unit 1 isretained in the oxygen mask 20. At this time, the ear straps 12, 13connected to the sensor main unit 1 are fastened around the ears 14.

Even the present example yields the same operation and working effect asthose yielded in the first example shown in FIG. 3.

FIG. 9 is a perspective view showing a fourth example of the retainingmeans. In this example, the sensor main unit 1 is attached to andretained on the exterior surface of the oxygen mask 20 attached to theface. As shown in FIG. 9, the sensor main unit 1 is fixed to a positionon the exterior surface of the oxygen mask 20 where a respiratory holeis to be formed, by way of an annular adapter 24. The sensor main unit 1measures a carbon dioxide gas in the respiratory gas from the oxygenmask 20.

Even the present example yields the same operation and working effect asthose yielded in the first example shown in FIG. 3.

FIG. 10 is a partially cutaway front view showing an example in which arespiratory guide section 25 is provided at the entrance of therespiratory flow path 4 of the sensor main unit 1 for guiding exhaledgas to the respiratory flow path 4. The respiratory guide section 25 hasthe shape of a funnel which can be brought into intimate contact with anarea of the face located below the nose.

In the example, a respiratory gas can be introduced into the respiratoryflow path 4 without fail. Even if one of the nostrils 15 has beenclogged, a carbon dioxide gas in the respiratory gas can be detectedwithout fail.

FIG. 11 is a perspective view showing another example configuration ofthe respiratory guide section. In the example, an air guide for nasalrespiration 26 and an air guide for oral respiration 27 are fixed to theouter periphery of the respiratory flow path 4 of the sensor main unit1. The air guide for nasal respiration 26 has the shape of a funnel, andnotches 26 a are formed in the center positions of respective sides ofthe air guide 26, thus enabling insertion of the nose. The notch 26 amay be formed in one side of the air guide 26 facing the living body,and there may be obviated a necessity for forming the notch 26 a in theother side. Depending on the height of the air guide for nasalrespiration 26, the notches 26 a formed in both sides of the guidesection may be obviated.

The air guide for oral respiration 27 is situated so as to oppose themouth when the sensor main unit 1 is attached to the face and is formedinto a plate warped toward the mouth. Alternatively, only either the airguide for nasal respiration 26 or the air guide for oral respiration 27may be provided on the sensor main unit 1.

FIGS. 12 through 15 show examples of the third invention. FIG. 12 is atransverse cross-sectional view; FIG. 13 is a longitudinalcross-sectional view; FIG. 14 is an exploded perspective view; and FIG.15 is a perspective assembly view of the principal features. As shown inthese drawings, both lateral sides of an airway case 41 formed into arectangular-parallelepiped shape are opened. A circular hole 41 a isformed in the upper surface of the airway case 41 so that an adapter,which is thin circular shaped, to be described later is to be insertedinto the hole. Further, a rectangular ventilating hole 41 b is formed inthe lower surface of the airway case 41. An adapter 43—on which twoflexible nasal insertion prongs 42 made of, e.g., silicone rubber, areprovided in an upright position—is fittingly attached to an adapterreception 41 d provided on the upper surface of the airway case 41.Lower ends of the nasal prongs 42 are brought in communication with theinside of the airway case 41.

An anti-fogging film 44 which is a thin film is provided on each of thelateral sides of the airway case 41. A anti-fogging film case 45 isdisposed outside of the each anti-fogging film 44 as a holding member. Astep section 45 a to be fitted into the inner periphery of one side ofthe air way case 41 is formed in an outer periphery at one end of theanti-fogging film case 45. The anti-fogging films 44 are pressed againstthe respective lateral sides of the airway case 41 by the anti-foggingfilm case 45. The steps 45 a are fitted to the internal circumferencesof the lateral sides so that the anti-fogging films 44 can behermetically fastened to the airway case 41. A hook 41 c—with which anair adapter for oral respiration to be described later is engaged—isprovided on one side of the airway case 41.

Arms 45 b are formed integrally with both sides of the anti-fogging filmcase 45 so as to project in the direction opposite to the step section45 a. An engagement hole 45 c is formed in the vicinity of extremity ofeach arm 45 b. A V-shaped notch 45 d is formed in the center of thelower surface of the anti-fogging case 45 which opens in the samedirection in which the arms 45 b extend.

A light-emitting section 46 is attached to the outer side of one of theanti-fogging film cases 45, and a light-receiving section 47 is attachedto the outer side of the remaining anti-fogging film case 45. Thelight-emitting section 46 is constituted of a rectangular-parallelepipedshaped light-emitting section case 51 serving as a support member forhousing a light-emitting element 48, a reflecting mirror 49, and awindow 50 made of sapphire in an aligned manner. Further, thelight-receiving section 47 is constituted of arectangular-parallelepiped shaped light-receiving section case 54serving as a support member for housing a light-receiving element 52 anda window 53 made of sapphire in an aligned manner. A lead wire 55connected to the light-emitting element 48 is led to the outside of thecase 51 via a socket 57. Similarly, a lead wire 56 connected to thelight-receiving element 52 is led to the outside of the case 54 via asocket 58.

A hook 51 a is provided on either side surface of the light-emittingsection case 51. A projection 51 b is provided on the upper surface ofthe light-emitting section case 51. When the light-emitting section case51 is fitted into the space defined between the arms 45 b of theanti-fogging film case 45, the hook 51 a is engaged with and locked bythe engagement holes 45 c formed in the respective arms 45 b. Theprojection 51 b provided on the upper surface of the light-emittingsection case 51 is brought into contact with and positioned by the upperend face of the anti-fogging film case 45. Further, a triangularprojection 51 c is provided on the lower surface of the light-emittingsection case 51. At the time of assembly, the projection 51 c is engagedwith and positioned by the notch 45 d formed in the lower end face ofthe anti-fogging film case 45. A hook 54 a and projections 54 b, 54 c,which operate in the same manner as the hook 51 a and the projections 51b, 51 c, are formed on the light-receiving section case 54.

An air guide for oral respiration 59 is removably attached to one sidesurface of the airway case 41. The air guide for oral respiration 59 isformed from, e.g., flexible polypropylene, into the shape of a spoon. Ahole 59 a is formed in an upper part of the air guide for oralrespiration 59 so that the hook 41 c formed on the airway case 41 isfitted to the hole.

According to this example, the light-emitting section case 51 and thelight-receiving section case 54 are removably attached to the airwaycase 41. Hence, bonding of the windows 50, 53 made of sapphire to thecorresponding cases 51, 54 is facilitated, thus improving productivity.Further, cleaning of the airway case 41 is also made easy.

The foregoing configuration example has described a case whererespiratory gas from the nose is introduced to the airway case 41 viathe nasal prongs 42. Alternatively, the adapter 43 having the nasalprongs 42 may be omitted, and respiratory gas may be introduced directlyinto the airway case 41. If the air guide for oral respiration 59 is notnecessary, it may be omitted.

As has been described, a sensor for measuring the concentration orpresence/absence of carbon dioxide in respiratory gas from a living bodyaccording to the present invention comprises a support member forsupporting a light-emitting element and a light-receiving element whichare disposed on a single optical axis so as to oppose each other; and arespiratory flow path which is formed in the support member and throughwhich respiratory gas can flow so as to cross over the optical axis whenthe support member is attached to an area located below the nostrils orto an oxygen mask covering the face of the living body. Hence, an airwayadapter and a sampling tube, which have hitherto been used, becomeunnecessary, thereby rendering the sensor compact and less-expensive.Further, measurement accuracy and response of the sensor are improved.Moreover, since the power consumed by the light-emitting element is madesmaller, a temperature rise becomes smaller, thus obviating a risk ofoccurrence of a burn.

What is claimed is:
 1. A sensor, adapted to be attached on a human bodyto measure concentration or presence/absence of carbon dioxide inrespiratory gas from the human body, the sensor comprising: alight-emitting element, operable to emit light; a light-receivingelement, configured to receive the light; a support member, supportingthe light-emitting element and the light-receiving element, andconfigured to be brought into contact with a part between nostrils and amouth of the human body when the sensor is attached on the human body;and a respiratory flow path formed in the support member andintersecting between the light-emitting element and the light-receivingelement, the respiratory flow path being configured to allow therespiratory gas to pass therethrough when the support member is broughtinto contact with the part between the nostrils and the mouth, wherein awidth of the support member in a direction perpendicular to a lineextending between the light-emitting element and the light-receivingelement is smaller than a distance between the nostrils and the mouth.2. The sensor as set forth in claim 1, wherein the respiratory path isconfigured to allow the respiratory gas from the human body to passbetween the light-emitting element and the light-receiving element andthen to be out from the support member, when the support member isbrought into contact with the part between the nostrils and the mouth.3. The sensor as set forth in claim 1, further comprising an engagementmember, provided on the support member and configured to be engaged witha tubular member for supplying oxygen to the nostrils.
 4. The sensor asset forth in claim 1, further comprising a mouth-side guide member,provided on the support member and configured to guide respiratory gasfrom the mouth to the respiratory flow path when the sensor is attachedto the human body.
 5. The sensor as set forth in claim 1, furthercomprising a nasal-side guide member, configured to guide respiratorygas from the nostrils to the respiratory flow path when the sensor isattached to the human body.
 6. The sensor as set forth in claim 5,wherein the nasal-side guide member has two nasal prongs configured tobe inserted into the nostrils when the support member is brought intocontact with the part between the nostrils and the mouth.
 7. The sensoras set forth in claim 5, wherein the nasal-side guide member comprises afunnel-shaped member.
 8. An airway case, adapted to be attached on ahuman body and adapted to support a light-emitting element and alight-receiving element to measure concentration or presence/absence ofcarbon dioxide in respiratory gas from the human body, the airway casecomprising: a support member, having a first part configured to supportthe light-emitting element and a second part configured to support thelight-receiving element, the support member being configured to bebrought into contact with a part between nostrils and a mouth of thehuman body when the airway case is attached on the human body; and arespiratory flow path formed in the support member and intersectingbetween the first part and the second part, the respiratory flow pathbeing configured to allow the respiratory gas to pass therethrough whenthe support member is brought into contact with the part between thenostrils and the mouth, wherein a width of the support member in adirection perpendicular to a line extending between the light-emittingelement and the light-receiving element is smaller than a distancebetween the nostrils and the mouth.
 9. The airway case as set forth inclaim 8, wherein the respiratory path is configured to allow therespiratory gas from the human body to pass between the light-emittingelement and the light-receiving element and then to be out from thesupport member, when the support member is brought into contact with thepart between the nostrils and the mouth.
 10. The airway case as setforth in claim 8, further comprising an engagement member, provided onthe support member and configured to be engaged with a tubular memberfor supplying oxygen to the nostrils.
 11. The airway case as set forthin claim 8, further comprising a mouth-side guide member, provided onthe support member and configured to guide respiratory gas from themouth to the respiratory flow path when the airway case is attached tothe human body.
 12. The airway case as set forth in claim 8, furthercomprising a nasal-side guide member, configured to guide respiratorygas from the nostrils to the respiratory flow path when the airway caseis attached to the human body.
 13. The airway case as set forth in claim12, wherein the nasal-side guide member has two nasal prongs configuredto be inserted into the nostrils when the support member is brought intocontact with the part between the nostrils and the mouth.
 14. The airwaycase as set forth in claim 12, wherein the nasal-side guide membercomprises a funnel-shaped member.
 15. The sensor as set forth in claim1, wherein the support member further comprises a first housing portionand a second housing portion, the first housing portion enclosing thelight-emitting element and the second housing portion enclosing thelight-receiving element, the first housing portion and the secondhousing portion are connected by a connecting member extending betweenthe first housing portion and the second housing portion and that isconnected to a back side of each of the first housing portion and thesecond housing portion, and a volume defined by the first housingportion, the second housing portion and the connecting member isexternally open to receive respiratory air from a top side, a bottomside and a front side of the volume.
 16. The airway case as set forth inclaim 8, wherein the first part and the second part are connected by aconnecting member extending between the first part and the second part,the connecting member is connected to a back side of each of the firstpart and the second part, and a volume defined by the first part, thesecond part and the connecting member is externally open to receiverespiratory air from a top side, a bottom side and a front side of thevolume.
 17. The sensor as set forth in claim 1, wherein the supportmember has a length longer than a width, and the width of the supportmember is configured to fit between the nostrils and the mouth.
 18. Theairway case as set forth in claim 8, wherein the support member has alength longer than a width, and the width of the support member isconfigured to fit between the nostrils and the mouth.